Conventionally, nuclear medicine imaging apparatuses, such as single photon emission computed tomography (SPECT) apparatuses and positron emission computed tomography (PET) apparatuses, are known as medical image diagnostic apparatuses that can perform functional diagnosis of the living tissue of a subject. Specifically, a nuclear medicine imaging apparatus detects, using a detector, gamma rays, which are emitted from an isotope or a labeled compound a selectively absorbed by living tissue, and then reconstructs nuclear medicine images which depict the radiation dose distribution of the detected gamma rays.
In recent years, apparatuses such as PET-CT apparatuses and SPECT-CT apparatuses have been put to practical use that are combinations of nuclear medicine imaging apparatuses and X-ray computed tomography (CT) apparatuses, which image morphological information on a living tissue of a subject. While rotating an X-ray tube and an X-ray detector about the body axis of a subject, an X-ray CT apparatus radiates X-rays from the X-ray tube to the subject and detects the X-rays that pass through the subject, thereby reconstructing images (X-ray CT images) that visualize the tissue morphology of the X-ray irradiated part of the subject.
X-ray CT apparatuses, however, generate more X-rays than gamma rays detected by PET apparatuses or SPECT apparatuses. In other words, with PET-CT apparatuses or SPECT-CT apparatuses, when acquiring X-ray CT images, scattered radiation of the X-rays generated by an X-ray CT apparatus are incident on the gamma ray detector. The incident scattered radiation may exceed the dynamic range of measurement for acquiring nuclear medicine images. When the measurement dynamic range is exceeded, a load is applied to the circuit that is connected to the gamma ray detector.